即使我包含了 unistd.h，在内核代码中也隐式声明了 getpid

Question

I'm currently working on a project that includes using PIDs. When I compile my program in a linux VM, I get the following message:

kernel/sys.c:2405: error: implicit declaration of function ‘getpid’
kernel/sys.c:2407: error: implicit declaration of function ‘getpriority’

even though I have included:

#include <asm/unistd.h>

in my code.

I have also tried to use types.h , but that does not work either.

Here is a snippet of the erroneous code, if it might help:

if(new_process != NULL){
            pid = getpid(new_process->p);
            pid2 = getpid(sem->head);
            p = new_process->p;
            if(getpriority(which, pid) > getpriority(which, pid2)){
                new_process->next = p;
                sem->head = p;

Any suggestions are welcome, and thanks for your help.

Answer 1

As I understand, you're working with kernel code. There's no C standard library in the kernel! You don't have getpid() , getpriority() , or any other standard library function or header (some very common functions like strlen() are re-defined in the kernel, but not all of them). To achieve what you want, you'll have to use the appropriate equivalent kernel APIs, which are usually more low level.

Assuming that new_process->p and sem->head are struct task_struct , you can get their priority with the task_nice() function defined in linux/sched.h (which is exactly what the getpriority syscall does, if you take a look at the code ).

Your snippet could be then re-written like this:

if(new_process != NULL) {
    p = new_process->p;
    if(task_nice(p) > task_nice(sem->head)) {
        new_process->next = p;
        sem->head = p;

If for some reason you also need the PID, you can access it directly through p->pid , as it is a field of struct task_struct .